ucm: add ${eval:EXPR} substitution (Syntax 5)

It is useful to do simple integer math in UCM configurations, too.
Use snd_config_evaluate_string() string for this job.

Example:

    ${eval:1+1}
    ${eval:100*$var1}
    ${eval:$[$var2+1]/5}

Signed-off-by: Jaroslav Kysela <perex@perex.cz>

src/confeval.c

@@ -119,8 +119,8 @@ static int _to_integer(value_type_t *val, snd_config_t *c)
 	return 0;
 }
 
-static int _eval_string(snd_config_t **dst, const char *s,
+int _snd_eval_string(snd_config_t **dst, const char *s,
-			snd_config_expand_fcn_t fcn, void *private_data)
+		     snd_config_expand_fcn_t fcn, void *private_data)
 {
 	snd_config_t *tmp;
 	const char *save, *e;
@@ -174,7 +174,7 @@ static int _eval_string(snd_config_t **dst, const char *s,
 					return -ENOMEM;
 				memcpy(m, s + 2, e - s - 2);
 				m[e - s - 3] = '\0';
-				err = _eval_string(&tmp, m, fcn, private_data);
+				err = _snd_eval_string(&tmp, m, fcn, private_data);
 				free(m);
 				if (err < 0)
 					return err;
@@ -250,7 +250,7 @@ int snd_config_evaluate_string(snd_config_t **dst, const char *s,
 	if (*s != '$')
 		return -EINVAL;
 	if (s[1] == '[') {
-		err = _eval_string(dst, s, fcn, private_data);
+		err = _snd_eval_string(dst, s, fcn, private_data);
 		if (err < 0)
 			SNDERR("wrong expression '%s'", s);
 	} else {

src/ucm/ucm_local.h

@@ -40,7 +40,7 @@
 #include <pthread.h>
 #include "use-case.h"
 
-#define SYNTAX_VERSION_MAX	4
+#define SYNTAX_VERSION_MAX	5
 
 #define MAX_CARD_SHORT_NAME	32
 #define MAX_CARD_LONG_NAME	80

src/ucm/ucm_subs.c

@@ -585,6 +585,42 @@ static char *rval_var(snd_use_case_mgr_t *uc_mgr, const char *id)
 	return NULL;
 }
 
+int _snd_eval_string(snd_config_t **dst, const char *s,
+		     snd_config_expand_fcn_t fcn, void *private_data);
+
+static int rval_eval_var_cb(snd_config_t **dst, const char *s, void *private_data)
+{
+	snd_use_case_mgr_t *uc_mgr = private_data;
+	const char *v;
+
+	v = uc_mgr_get_variable(uc_mgr, s);
+	if (v == NULL)
+		return -ENOENT;
+	return snd_config_imake_string(dst, NULL, v);
+}
+
+static char *rval_eval(snd_use_case_mgr_t *uc_mgr, const char *e)
+{
+	snd_config_t *dst;
+	char *r;
+	int err;
+
+	if (uc_mgr->conf_format < 5) {
+		uc_error("variable substitution is supported in v5+ syntax");
+		return NULL;
+	}
+	err = _snd_eval_string(&dst, e, rval_eval_var_cb, uc_mgr);
+	if (err < 0) {
+		uc_error("unable to evaluate '%s'", e);
+		return NULL;
+	}
+	err = snd_config_get_ascii(dst, &r);
+	snd_config_delete(dst);
+	if (err < 0)
+		return NULL;
+	return r;
+}
+
 #define MATCH_VARIABLE(name, id, fcn, empty_ok)				\
 	if (strncmp((name), (id), sizeof(id) - 1) == 0) { 		\
 		rval = fcn(uc_mgr);					\
@@ -688,6 +724,7 @@ __std:
 		MATCH_VARIABLE2(value, "${env:", rval_env, false);
 		MATCH_VARIABLE2(value, "${sys:", rval_sysfs, false);
 		MATCH_VARIABLE2(value, "${var:", rval_var, true);
+		MATCH_VARIABLE2(value, "${eval:", rval_eval, false);
 		MATCH_VARIABLE2(value, "${find-card:", rval_card_lookup, false);
 		MATCH_VARIABLE2(value, "${find-device:", rval_device_lookup, false);
 		MATCH_VARIABLE2(value, "${CardNumberByName:", rval_card_number_by_name, false);